1. Field of the Invention
The present invention relates to a head position control method of a disk storage device and a disk storage device which uses a disk as an information recording medium, moves a head in a radius direction of the disk, and reads information recorded on the disk, and more particularly to a head position control method and disk storage device for reading servo information of the disk and controlling the position of the head.
2. Description of the Related Art
Information storage devices using such recording medium as a magnetic disk, optical disk, and magneto-optical disk are widely used. In such an information storage device, a read or read/write head is positioned at a predetermined track of a disk for reading or writing data.
FIG. 10 is a diagram depicting the servo-information of a conventional disk, FIG. 11 is a diagram depicting a head positioning control system of a conventional disk device, and FIG. 12 is a diagram depicting a conventional speed detection operation.
As FIG. 10 shows, in the case of a head positioning control system called a sector servo system used for a magnetic disk device, servo areas 102, where servo information is recorded on each sector 103 on the disk 100, are arranged radially at an equal angle. The head is positioned on the target track of the disk 100 based on this servo information. Tracks are created concentrically on a magnetic disk, and tracks are created in spirals on an optical disk.
The servo information 102 is comprised of a track address and a position information signal pattern. The track address is used for recognizing each track. And the position information signal pattern is used for determining the offset amount of the head from the center of the track.
As FIG. 11 shows, the magnetic disk device is comprised of a magnetic disk 100 which rotates, a magnetic head 110, and an actuator 120 which moves the magnetic head 110 in a radius direction of the magnetic disk 100. The position detection circuit 130 detects the position of the head 110 at every predetermined time by the servo information which the head 110 reads when the head passes through the servo area 102.
To read and write data on the disk 100, the head position control section 150 first moves the head 110 to the target track (this is called seek). Then the head 110 is followed up onto the target track until the head 110 reaches the target sector (this is called following), and when the head comes to the target sector, the head 110 writes or reads the data.
For the control to move the head 110 to the target track (seek control), speed control is generally performed. Now the flow of the control of the head position control section 150 will be described.
(1) The position detection circuit 130 detects the current head position from the servo information read by the head 110.
(2) The speed calculation circuit 140 calculates the current head speed using the head positions of the past and the current.
(3) The head position controlling section 150 calculates the target speed from the remaining distance.
(4) The head position controlling section 150 determines the difference between the target speed and the current speed, provides the result to the compensator, and calculates the current command value. The actuator 120 is driven by this current command value.
By repeating the above operation, the head is moved to the target track.
In prior art, the head speed is estimated from the position of the head instead of directly detecting the head speed. To calculate this head speed, the speed is determined by differentiating the position, as shown in FIG. 12. In other words, in the case of sample servo control, the position is detected at each predetermined interval T, and the speed is calculated by dividing the difference between the position sampled the previous time and the position sampled this time by the interval T.
However if there is an error in the information of the detected head position, the high frequency component of the positional error is emphasized as the error of the speed by the differential operation. Also in order to estimate the speed from the sampled position signals, it is regarded that the head moved for the difference between the position of the previous sampling and the position of this sampling during the sampling time, so the average speed between the previous sampling and this sampling is known the first time when the head position is sampled this time, which means that the speed is measured with a delay of the half time of the sampling time.
Such an error of the detection speed and the actual speed drops the follow up accuracy to the target speed, and decreases the phase margin of the control system. Therefore if the head movement at a higher speed is attempted, the control system becomes unstable, a high-speed seek operation and the following operations become difficult, and an increase in the speed of the track accessing time is made difficult.